http://repositorio.ufc.br/handle/riufc/169 Tue, 14 Apr 2026 05:33:30 GMT 2026-04-14T05:33:30Z http://repositorio.ufc.br/handle/riufc/85730 Título: Ácido adipico em condições extremas de temperatura e pressão Autor(es): Silva, Rômulo Sampaio da Abstract: Dicarboxylic acids are organic compounds characterized by the presence of two carboxyl groups (COOH) in their molecular structure, which are responsible for their acidity. These compounds are found in more complex organic systems and play important roles in various chemical and biological processes. In addition, they attract significant interest due to their wide applicability in different industrial fields, making it essential to understand their physical and chemical properties under varying temperature and pressure conditions. In this context, this work investigates the structural behavior of adipic acid C6H10O4 under extreme temperature and pressure conditions through a combination of Raman spectroscopy, powder X-ray diffraction, and density functional theory (DFT) calculations. Initially, vibrational characterization was carried out under ambient conditions, allowing the classification and assignment of the observed modes with the support of computational calculations performed on the unit cell. At low temperatures, the sample was cooled down to 10 K, where a phase transition previously reported in the literature was observed in the range between 135 K and 130 K, accompanied by crystal fragmentation and significant changes in the Raman spectrum. In order to better understand these results, powder X-ray diffraction measurements were performed, revealing phase coexistence below the transition temperature, persisting down to approximately 10 K. Under high pressures, the sample was investigated up to values above 7 GPa in two independent Raman spectroscopy experiments. Significant changes in intermolecular vibrational modes, together with an increase in the number of modes above 1.6 GPa, indicated a phase transition associated with a reduction in the symmetry of the crystal structure. At higher pressures, variations in the intensities of internal modes suggest possible conformational changes of the molecules within the unit cell. The results obtained highlight the strong dependence of adipic acid on thermodynamic conditions, contributing to the understanding of phase transition mechanisms in this molecular system. Tipo: Tese Thu, 01 Jan 2026 00:00:00 GMT http://repositorio.ufc.br/handle/riufc/85730 2026-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/85588 Título: Estudo das propriedades vibracionais das perovskitas híbridas de azida Autor(es): Hora, Renata Rodrigues da Abstract: Recently, perovskite-type organic-inorganic hybrid compounds have attracted considerable interest due to their structural versatility, which allows for the manifestation of various interesting physical properties for application in devices. These materials exhibit a wide range of functionalities, including photovoltaic, ferroelectric, and multiferroic properties. In this thesis, we used the slow evaporation method to obtain three perovskite-type hybrid compounds, [(CH3)3N][Mn(N3)3] (TrMAMnN3), [(CH3)2NH][Mn(N3)3] (DMAMnN3), [(CH3)2NH]2[CoNa(N3)6], whose structural, thermal, and vibrational properties were investigated as a function of temperature. In the case of the compound [(CH3)3NH][Mn(N3)3], we analyzed in detail the wavenumber and full-width half-height (FWHM) of lattice modes and internal modes of the NC3 skeleton, N3– and CH3 molecular groups. In general, the modes exhibited unusual behavior during phase transitions, including discontinuity in phonon wavenumber, bandwidth, and unconventional changes due to temperature variation. Furthermore, we used differential scanning calorimetry (DSC) to confirm a subtle monoclinic-to-monoclinic phase transition (P21/c →C2/c) around 330 K; and the phase transition to trigonal structure (R m) above 359 K, whose associated entropy variation becomes |ΔS| ~ 22.3 J·kg⁻¹ K⁻¹ and exhibits a barocaloric coefficient (BC) |δTt/δP| ~ 3.17 K kbar⁻¹. For DMAMnN₃, a first-order structural transition from the orthorhombic phase (Cmca) to the monoclinic phase (P2₁) was identified, with an entropy variation of ~37.2 J·kg⁻¹·K⁻¹ and a barocaloric coefficient of ~2.94 K·kbar⁻¹, in agreement with the Clausius-Clapeyron method. Room-temperature Fourier transform infrared (FTIR) reflectivity spectra identified polar phonons and their damping coefficients. Minimal contributions from the DMA+ mode were observed in the intrinsic dielectric constant (~4.3). An anomaly was observed at ~85 K, indicating a transition from the paramagnetic to the antiferromagnetic state (PM-AFM). Finally, we present a new compound obtained through the slow evaporation synthesis [(CH3)2NH]2[CoNa(N3)6], where single-crystal XRD measurements resolved the material's structure, showing that up to 100 K the structure does not exhibit a structural phase transition. A room-temperature Raman spectrum was also obtained, and mode assignment was performed. Tipo: Tese Thu, 01 Jan 2026 00:00:00 GMT http://repositorio.ufc.br/handle/riufc/85588 2026-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/85551 Título: Condições de contorno para nanofitas de fosforeno com bordas enviesadas Autor(es): Costa, Tiago da Silva Abstract: Phosphorene, a monolayer of black phosphorus, exhibits a honeycomb-like structure in top view and a puckered structure in other directions. This is due to sp3 hybridization, in which each phosphorus atom establishes three covalent bonds with neighboring atoms in the monolayer. As a result, phosphorene-based nanostructures can present different edge terminations, called normal and skewed, of the zigzag and armchair type. In the effective theoretical description of the phosphorene monolayer, the literature provides tight-binding models that account for two, five, or ten hopping interactions. Initially, this research employed these models to describe the band structure of the infinite system, exploring the role of each energetic connection between sites in the three theoretical models. It was found that adjustments in the interaction strengths, in-plane and out-of-plane, can drastically change the electronic dispersions of the system’s energy bands. Subsequently, using the three tight-binding models, phosphorene nanoribbons with different widths and distinct edge termination types were studied: normal zigzag, normal armchair, skewed zigzag, and skewed armchair. Results on the dispersion relations and wave functions of edge states were discussed. It was verified, for the case of nanoribbons with normal zigzag and skewed armchair edges, that adjustments in the interaction contributions allow quasi-flat edge states to become perfectly flat. As a perspective, it is intended to employ the continuum approximation, derived from the Taylor series expansion around the Γ point of the tight-binding model, to describe the electronic properties of different phosphorene nanoribbons. To this end, suitable boundary conditions will be proposed to describe the electronic properties of phosphorene nanoribbons with skewed and normal edges. The analytical results can then be compared with those provided by the tight-binding models. Finally, we seek to demonstrate the dependence of the bandgap on the width of the nanoribbons. Tipo: Dissertação Thu, 01 Jan 2026 00:00:00 GMT http://repositorio.ufc.br/handle/riufc/85551 2026-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/85550 Título: Escoamento bifásico em meio poroso: análise dos regimes do estado estacionário Autor(es): Magalhães, Alessandro Peixoto Abstract: Immiscible displacement in disordered porous media exhibits a wide range of steady-state interfacial morphologies whose collective organization cannot be inferred from transport laws alone. These patterns arise from the competition between viscous, capillary, and inertial forces; however, descriptions that span different regimes and simultaneously connect dimensionless control parameters, morphology, and collective structure remain limited. In this work, we simulate the Navier-Stokes equations with periodic boundary conditions to resolve statistically steady two-phase flow in a disordered porous matrix consisting of a random array of non-overlapping disks, over wide ranges of pressure gradient and interfacial tension, covering multiple orders of magnitude in the Capillary and Forchheimer numbers. Using unsupervised machine learning, we identify three robust steady-state morphologies — bubbles, stripes, and mixtures — organized in a regime diagram (Fo, Ca) with sharp and consistent transitions governed by the balance between capillary, viscous, and inertial effects. Despite these pronounced morphological reorganizations, macroscopic transport varies smoothly: stripe and mixture states follow a Forchheimer-type V versus |∇p| relation, while bubble states deviate systematically due to the additional energy barrier arising from interface deformations. To characterize the collective organization underlying these morphologies, and following the precedent of pseudo-thermodynamic analogies for two-phase flows, we coarse-grain steady-state configurations into binary fields and infer pairwise maximum-entropy models. The inferred Hamiltonians reproduce the fitted first- and second-order statistics and, near some morphological transitions, accurately predict out-of-sample higher-order correlations. Thermodynamic analysis of the inferred models—in which temperature is a parameter of the statistical model, unrelated to the physical temperature of the fluid—reveals regime-dependent specific heat signatures: a considerable fraction of stripe morphologies operate near an order-disorder transition point, while bubble and mixture states correspond to supercritical organization. Taken together, the hydrodynamic regime map and the maximum-entropy representation establish a unified, dimensionless framework connecting interfacial morphology, macroscopic transport, and collective statistics in two-phase porous flows. Tipo: Dissertação Thu, 01 Jan 2026 00:00:00 GMT http://repositorio.ufc.br/handle/riufc/85550 2026-01-01T00:00:00Z